Frequently Asked Questions (FAQ)

Welding Methods for Steel Structures

# Common Welding Methods for Steel Structures

The commonly used welding method for steel structures is **arc welding**, including **manual arc welding**, **automatic or semi-automatic arc welding**, and **gas-shielded arc welding**. **Manual arc welding** is the most widely used in steel structures. It features simple equipment and flexible operation. However, working conditions are poor, production efficiency is lower than that of automatic or semi-automatic welding, and weld quality varies greatly, depending to a certain extent on the welder’s skill level. **Automatic welding** provides stable weld quality, fewer internal defects, good ductility and impact toughness, and is suitable for long, straight welds. **Semi-automatic welding**, involving manual operation, is suitable for curved or arbitrarily shaped welds. Both automatic and semi-automatic welding shall use welding wires and fluxes compatible with the base metal. Welding wires shall comply with national standards, and fluxes shall be selected according to welding process requirements. **Gas-shielded arc welding** uses inert gas or CO₂ as the shielding medium to isolate molten metal from air and maintain a stable welding process. It features concentrated arc heating, high welding speed and deep penetration, resulting in higher weld strength than manual welding. It also offers good ductility and corrosion resistance, making it suitable for welding thick steel plates. ## I. Weld Types According to the relative positions of connected members, welded connections can be classified into four types: **butt joint, lap joint, T-joint, and corner joint**. The welds used in these connections fall into two basic types: **butt welds** and **fillet welds**. In practical applications, selection shall be based on the stress conditions of the connection, combined with fabrication, installation and welding conditions. ## II. Weld Details ### 1. Butt Welds Butt welds transfer force directly and smoothly without significant stress concentration, thus providing good mechanical performance. They are suitable for member connections under static or dynamic loads. However, due to high quality requirements and strict clearance requirements between workpieces, they are generally used for shop-fabricated connections. ### 2. Fillet Welds **Forms of fillet welds**: According to the relationship between the length direction and the applied load, fillet welds can be divided into: - side fillet welds (parallel to the load), - front fillet welds (perpendicular to the load), - diagonal fillet welds (inclined to the load), - and wrap-around fillet welds. **Cross-sectional forms of fillet welds**: They are divided into **standard fillet, flat-slope fillet, and deep-penetration fillet**. - The standard fillet has a leg ratio of 1:1 (approximate isosceles right triangle), with sharp force flow deviation and severe stress concentration. - For structures directly subjected to dynamic loads, to ensure smooth force transmission, front fillet welds should adopt the flat-slope type with a leg ratio of 1:1.5 (long leg along the internal force), and side fillet welds should adopt the deep-penetration type with a ratio of 1:1.